Ultra sensitive magnetic field sensors

ABSTRACT

A magnetic sensor and magnetic field sensing method for ordnance, comprising locating a magnetoresistance detector within the ordnance and detecting magnetic fields with the detector. Also other sensing method and sensors employing such detectors.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation-in-part application of U.S.patent application Ser. No. 09/969,946, entitled ULTRA SENSITIVEMAGNETIC FIELD SENSORS, to Timothy C. Tiernan, et al., filed on Oct. 2,2001, which is a continuation-in-part application of U.S. patentapplication Ser. No. 09/265,991, entitled INTEGRATED MAGNETIC FIELDSENSORS FOR FUZES, to David W. Cutler, et al., filed on Mar. 9, 1999,issued on Oct. 2, 2001, as U.S. Pat. No. 6,295,931, which claimed thebenefit of the filing of U.S. Provisional Patent Application Serial No.60/077,525, entitled SENSITIVE INTEGRATED MAGNETIC FIELD SENSORS FORFUZES, filed on Mar. 11, 1998; and of U.S. Provisional PatentApplication Serial No. 60/092,717, entitled SENSITIVE INTEGRATEDMAGNETIC FIELD SENSORS FOR FUZES, filed on Jul. 14, 1998; and thespecifications thereof are incorporated herein by reference.

[0002] This application also claims the benefit of the filing of U.S.Provisional Patent Application Serial No. 60/301,786, entitled ULTRASENSITIVE MAGNETIC FIELD SENSORS, filed on Jun. 29, 2001, and thespecification thereof is incorporated herein by reference.

GOVERNMENT RIGHTS

[0003] The U.S. Government has a paid-up license in this invention andthe right in limited circumstances to require the patent owner tolicense others on reasonable terms as provided for by the terms ofContract No. SOL DAAE30-01-BAA-0500 and Contract No. DAAE30-99-C-1068awarded by the U.S. Army TACOM-ARDEC, by the terms of Contract Nos.DMI-0060397 and DMI-9704080 awarded by the National Science Foundation,and a contract with the U.S. Navy.

BACKGROUND OF THE INVENTION

[0004] 1. Field of the Invention (Technical Field)

[0005] The present invention relates to sensors made of giantmagnetoresistance materials (GMR), colossal magnetoresistive (CMR)materials, or anisotropic magnetoresistive (AMR) materials. The termsmagnetoresistance and GMR, as used throughout the specification andclaims, are intended to include giant, colossal, and anisotropicmagnetoresistance or magnetoresistive materials.

SUMMARY OF THE INVENTION (DISCLOSURE OF THE INVENTION)

[0006] The present invention is of a magnetic sensor and magnetic fieldsensing method for ordnance, comprising locating a giantmagnetoresistance detector within the ordnance and detecting magneticfields with the detector. In one embodiment, turns of spinning ordnanceare counted, with autonulling being employed, such as injecting a chargeinto a circuit comprising the giant magnetoresistance detector, thecharge injection being triggered upon exit or when a rate of spin of theordnance exceeds a predetermined rate. In another embodiment, ordnanceis armed a pre-determined time after exit of the ordnance from a weaponfiring the ordnance, which can involve one or more of the following:determining exit of the ordnance from a weapon firing the ordnance(preferably by detecting concentrated earth's magnetic field lines at anopening of a weapon firing the ordnance), determining exit velocity,determining proximity to metallic targets, and determining direction tometallic targets. Turns count and other information can be programmedinto the sensor using an inductive programmer or other approach, usingdata from the targeting system of the munitions delivery system, toenable programming of the sensor just before it is fired. In anotherembodiment, incoming munitions are detected either through purturbationof the earth magnetic field, or by their intrinsic magnetic properties,such as by employing a biasing magnet, employing an oscillationfrequency, employing a coil proximate the exterior or nose of theordnance, employing multiple detectors and triangulation means, and/oremploying an array of detectors. The detector is preferably fabricatedon a printed circuit board, hybrid circuit, or integrated circuit. Thesensor can also perform one or more of the following functions:outputting a signal characteristic of impact of the ordnance, employinga map of local magnetic fields to determining position and direction ofan object, detecting flying objects by looking for response to anemitted magnetic field, and determining eddy currents output by flyingobject traversing earth's magnetic field.

[0007] The present invention is also of a magnetic field sensor andsensing method for locating defects in objects in two or threedimensions, comprising providing to a sensor a giant magnetoresistancedetector and traversing the sensor over an object. In the preferredembodiment, one or more of the following functions are performed:measuring induced or intrinsic magnetic fields to determining type ofdefect, determining volume lost to defect, determining depth of defect,imaging the defect, determining dimensions of defect, and producingLissajous plots of amplitude versus phase for magnetic fields.

[0008] The present invention is further of a magnetic field sensor andsensing method for medical imaging, comprising providing to a sensor agiant magnetoresistance detector and traversing the sensor over apatient. In the preferred embodiment, one or more of the followingfunctions are performed: measuring electromagnetic activity in thepatient's heart, measuring electromagnetic activity in the patient'sbrain, performing biomagnetics analysis, performing nuclear magneticresonance imaging, and imaging skin defects or tissue anomolies.

[0009] The invention is additionally of a magnetometer and magnetometrymethod comprising providing a giant magnetoresistance detector andoperating the detector. In the preferred embodiment, one or more of thefollowing functions are performed: detecting conductive materials on asurface, detecting conductive materials beneath a surface, detectingconductive materials in a body of liquid, locating naval vessels,detecting electrical currents flowing through printed circuit boardtraces, detecting electrical currents flowing through integrated circuitcomponents, measuring amplitudes of electrical currents, and detectingbreaks in electrical conductors. Operation may be in DC detection modeor employing oscillating magnetic fields or ambient fields.

[0010] The present invention is also of a magnetic field sensing systemand method for locating defects in objects in two or three dimensions,comprising providing a sensor comprising a magnetoresistance detectorand sensing at a plurality of frequencies. In the preferred embodiment,defects at a plurality of depths in the objects (e.g., printed circuitboards) are sensed.

[0011] The invention is further of a magnetic field sensing system andmethod for imaging objects, comprising providing a magnetoresistancedetector, employing means for non-magnetic imaging, and analyzing imagesproduced by both the magnetoresistance detector and the means fornon-magnetic imaging. In the preferred embodiment, the means fornon-magnetic imaging comprises optical imaging means.

[0012] The invention is additionally of a system and method formechanical system identification, comprising providing amagnetoresistance detector and using the detector to sensecharacteristics of a passing mechanical system. In the preferredembodiment, the passing mechanical system is a vehicle. Output of themagnetoresistance detector is analyzed and compared to knowncharacteristics of one or more of the following: perturbations of theearth's field by a moving metallic object or vehicle; fields associatedwith electric motors; fields associated with generators and alternators;fields associated with spark plugs, wires and coils; fields related torapidly moving metallic parts; and fields associated with large massesof metals. Preferably at least three magnetoresistance detectors areemployed. The detector can detect perturbations of the earth's magneticfield by the mechanical system, magnetic fields generated byelectromagnetic components of the mechanical system, and/or radio wavesgenerated by the mechanical system.

[0013] Objects, advantages and novel features, and further scope ofapplicability of the present invention will be set forth in part in thedetailed description to follow, taken in conjunction with theaccompanying drawings, and in part will become apparent to those skilledin the art upon examination of the following, or may be learned bypractice of the invention. The objects and advantages of the inventionmay be realized and attained by means of the instrumentalities andcombinations particularly pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The accompanying drawings, which are incorporated into and form apart of the specification, illustrate one or more embodiments of thepresent invention and, together with the description, serve to explainthe principles of the invention. The drawings are only for the purposeof illustrating one or more preferred embodiments of the invention andare not to be construed as limiting the invention. In the drawings:

[0015]FIG. 1 is an electrical schematic of the preferred spinning roundsensor of the invention;

[0016]FIG. 2 is a diagram of a circuit board incorporating the sensor ofthe invention;

[0017]FIG. 3 is a graph showing signal pulse upon exit from a mortartube of a munition incorporating the sensor;

[0018]FIG. 4 illustrates the sine wave detected by the sensor asgenerated by the rotation of a munition, with each cycle beingequivalent to one rotation of the munition;

[0019]FIG. 5 is an electrical schematic of the barrel exit detectionembodiment of the invention, useful with mortars and non-rotatingrounds;

[0020]FIG. 6 is a perspective view of a data logger PCB incorporatableinto a 40 mm round for testing purposes;

[0021]FIG. 7 is a front perspective view of a round incorporating datalogger and sensor PCBs just before final assembly;

[0022]FIG. 8 is a block diagram of a system useful in arming a deviceaccording to the invention and collecting data from an on-board dataacquisition system;

[0023]FIG. 9 illustrates a conditioned signal output by the data loggerPCB, each square wave transition corresponding to one revolution of the40 mm round;

[0024]FIG. 10 illustrates use of the sensor of the invention within acounter munition;

[0025]FIG. 11 is a perspective view of a handheld NDE unit includinggraphical modes that can resolve defects to a depth of more than 0.4″ in6061T6;

[0026]FIG. 12 is a top view of a 196-element tunnel junction imagingarray;

[0027]FIG. 13 is an 11 kHz C-scan of first and second layer rivet headsin an aluminum sheet metal section simulating an aircraft wing;

[0028]FIG. 14 shows 100 micron wide cuts in an aluminum sheet metalsample;

[0029]FIG. 15 is an APET image of a 10% mass loss corroded regionmeasured through 60 mils of aluminum, made from the side opposite thecorrosion;

[0030]FIG. 16 illustrates use of the sensor of the invention forguidance of a munition according to the invention to an under-sea mine;

[0031]FIG. 17 is a top view of a 14×14 element array of GMR sensorsproduced on a single substrate, each element being approximately 10×10microns;

[0032]FIG. 18 is output from a two-dimensional GMR sensor arrayaccording to the invention showing variations in magnetic field strengthover an area of metal; and

[0033]FIG. 19 is a block diagram of a system according to the inventionused for non-destructive evaluation of a sample.

DESCRIPTION OF THE PREFERRED EMBODIMENTS (BEST MODES FOR CARRYING OUTTHE INVENTION)

[0034] Magnetic Field Sensors For Munitions

[0035] The present invention is directed to an advanced, giantmagnetoresistive (GMR) based sensor platform for detection of spin rateand muzzle exit, muzzle exit velocity, range, proximity, attitude,and/or guidance of munitions from within the fuze assembly of anadvanced munition. The sensor can operate with both rotating rounds suchas a 40 mm rotating round or with non-rotating rounds such as a 60 mmmortar. The invention can also operate with finned munitions. The sensorcan be programmed at the time of firing using induction programmingtechniques or similar programming technology to cause the fuze system toactivate based on data obtained from a targeting system.

[0036] Extensive shock and thermal testing was employed to verify therobustness of the sensor. The sensor and support electronics weretransferred to a production board package in order to provide singleboard sensors for turns counting or barrel exit sensing. Live-fire testswere successfully completed for a 40 mm rotating round. The tests weresuccessful and showed that it is possible to monitor barrel exit,rotations, velocity, and range all with a single ambient field sensor.The results showed that the sensor was able to provide data that canmonitor munition flight distance with an error of less than 1% (0.84%).Evaluations of barrel exit detection, tolerance of mechanical shock, andenvironmental durability of the sensors were also positive using an 60mm mortar tube.

[0037] The preferred spinning round circuit design is as follows,including an autonulling capability (see FIG. 1). Upon setback oralternately as soon as the sensor begins to spin at a rate above a fewHz, the circuit injects a small charge into the sensor to compensate forany polling (due to large magnetic field exposure) that has taken placeduring storage of the sensor or munition. The rate of rotation foractivation is high enough that it will not null the sensor if themunition is dropped or rolled during handling. When fired, the rotationdue to rifling of the gun barrel makes the sensor spin at a sufficientrate, while the sensor is still in the barrel of the gun, to activatethe autonulling. This ensures that the sensor is biased properly todetect barrel exit when it is fired, and begin counting turns when themunition exits the barrel.

[0038] The circuit automatically nulls the GMR sensor during power-up.This compensates for any residual magnetization that may have occurreddue to close proximity of the sensor to large magnetic fields.

[0039] The circuits are preferably built on printed circuit boards(PCB), which offer low power operation in a small enough package to meetthe demands of both 40 mm rounds and 60 mm mortars. Circuits built thisway are much less expensive to design layout, build and test, than arecircuits made with hybrid techniques. However, hybrid circuits may beused where a smaller package is needed.

[0040] Shock testing was performed prior to firing the 40 mm testrounds. The sensor and electronics system were unaffected by exposure toshock. During live fire tests with 40 mm rounds the sensor andelectronics withstood the shock with no failures or any signs ofdamaging effects.

[0041] The present invention can also measure barrel exit time andbarrel exit velocity for mortars. Using techniques and sensors made fromgiant magnetoresistance materials (GMR), highly durable, low powersensors detect barrel exit in both 60 mm mortars, and 40 mm spinningrounds (FIGS. 2 and 5). Larger diameter mortars (e.g., 80 mm and 120 mm)require that the sensor have the ability to dependably detect the edgeof the mortar tube using a passive approach such as measuring theearth's magnetic field concentration at the edge (exit) of the mortar,or using an active mode, for example, a small permanent magnet mountedon the end of the mortar tube having a large distance between the sensorand the edge of the mortar tube. Laboratory tests with larger diametermortars indicate that the invention can measure both exit time and exitvelocity in these munitions.

[0042] The present invention also provides an advanced magnetic safingand arming (S&A) sensor technology based on giant magnetoresistivesensors. Extensive tests, including live fire tests with 40 mm munitionswere performed with both turns-counting and barrel-exit sensingconfigurations for rotating rounds. The present invention includesnon-rotating rounds, specifically 60 mm mortars. The sensors survivedrepeated mechanical shock tests in excess of 100,000 gs andenvironmental cycling ranging from 150 C to −180 C.

[0043] Tunnel-junction or spin valve GMR sensors with a resistancechange of 7-15% in a 2 Oe magnetic field applied perpendicular to theeasy axis of the device have been used. In general, high sensitivity tomagnetic field is desirable The sensor sizes used range from 0.4 mm×1 mmto 10 μm×10 μm. The device impedance used ranged from 100 Ω to 10 kΩ butother device impedances can be used depending on the application. Ingeneral high impedance (ohms per square) helps reduce the size of thesensor, and this saves power and reduces the size of the sensor. Thebandwidth of the sensor used was >1 Ghz, making it capable of detectingextremely rapid changes in magnetic fields. Power consumption of thesensor and support electronics is has been shown to be approximately 1milliamp at 3 volts for the spinning round sensor. Power requirementwill vary depending on the sensors and circuitry needed for eachapplication. The size of the sensor and its support electronics, mountedon a standard printed circuit board, is not an impediment since theentire assembly easily fits inside a 40 mm round or a 60 mm mortar fusewell without the need for modifications to the munition. If a smallersensor system is needed the sensor and circuit can be fabricated as ahybrid integrated circuit, greatly reducing the physical size of thesensor device.

[0044] In one embodiment, the sensor operates by detecting the magneticfield of the earth. In the case of a mortar round, the local fieldgradient is concentrated by the metal mortar tube. Inside the tube thereis little or no magnetic field. At the opening of the mortar tube, theearth's magnetic field lines are concentrated by the edges of the mortartube, resulting in a relatively strong field. When the mortar is fired,the sensor does not respond until it passes the end of the mortar tubewhere it detects the concentrated magnetic field. The sensor outputs anelectrical pulse that can be used as a trigger to mark barrel exit, andarm the mortar (FIG. 3).

[0045] In the case of a rotating round, the sensor is mounted such thatit spins along with the munition. As it spins, its sensitive axis cyclesfrom alignment with the earth's magnetic filed, to nonalignment. Thisresults in the sensor outputting a variable amplitude sine wavecorresponding to one revolution of the munition (FIG. 4). Since therifling dimensions for the gun from which the sensor is fired are known,it is possible to detect barrel exit, speed and range of the munition.

[0046] The sensor of the present invention has a wide range of usesincluding barrel exit and velocity for mortars. It can also be used fortrajectory measurements and proximity to metallic targets fornon-rotating rounds. The sensor system has highly desirablecharacteristics including: extremely small size, low power operation,high shock resistance, wide temperature range, and extremely fastresponse time. Its operation is based on the earth's magnetic fieldmaking it highly reliable and independent of other system such as GPS.The sensor system benefits munitions programs by offering a highperformance low cost alternative for arming and safing applications forboth non-rotating and rotating munitions.

[0047] Design of the Barrel Exit Sensor and Circuitry for a 120 mmMortar

[0048] Accurate barrel exit detection is related to the ambient noiselevel, signal state separation, and sensor bandwidth. The sensor outputwhen in the mortar tube compared to sensor output during barrel exit issufficient reliable barrel exit detection. If the sensor bandwidth ismuch smaller than the event bandwidth both event detection and timingaccuracy are degraded. Bandwidth, and signal output while inside themortar tube do not pose problems. The sensor can detect the threshold ofthe mortar tube where the earth's magnetic field is concentrated by themetal mortar tube.

[0049] Several techniques can be used to increase detection capabilityand reliability:

[0050] Using the same sensors described above for a 60 mm mortar,determine if there is sufficient sensitivity to detect barrel exit. Ifnot, refine the gain and frequency response of the circuitry to improveperformance as needed.

[0051] Use a more sensitive sensor and/or sensor arrays with extremelyhigh sensitivity.

[0052] Use a number of offset sensors each oriented in a differentdirection to determine if any one of them or any combination of themdetect the concentrated field at the mouth of the mortar tube. Thisarray of sensor can be read in a logical mode (e.g., AND, OR) toincrease the detection capabilities and reliability of the sensorconfiguration.

[0053] Use permanent magnet in conjunction with the sensor. For example,a permanent magnet may be placed at the end of the mortar tube where thefield would be detected by the sensor(s) as the munition exits themortar tube.

[0054] The preferred barrel exit circuitry (see FIG. 5) is preferablysimilar to the electronics developed and tested for mortar exit andspinning rounds. In its simplest form, the circuit has a self-nullingcapability so that when it is activated by powering the sensor, the biaspoint of the sensor is set to the center of its full range output. Thecircuit will then continuously compare the real-time output of thesensor to a preset voltage that corresponds to the output of the sensorunder low magnetic field conditions.

[0055] When the sensor (and mortar) exit the mortar tube, the sensordetects the earth's magnetic field concentrated at the mouth of thelaunch tube (barrel). When the sensor detects the magnetic fieldconcentration, its output causes the on-board detection circuitry tocross a preset comparison voltage. To accomplish the same goal, thesensor may also detect permanent magnets mounted at the end of thelaunch tube. This results in a high-speed digital pulse that is used totrigger the fuzing system. If two sensors are used with a known distancebetween the sensors, then the speed of the munition can be determined atbarrel exit. This information can be used for range analysis andcompensation due to weather, wind, or other conditions. Additionalfiltering circuitry may be used so that the sensor amplifier respondsonly to high frequency pulse characteristic of high-speed barrel exit.This helps eliminate noise and other spurious signals due to set back,permanent magnetic fields in the mortar tube, and accidental dropping ofthe mortar round or low speed exit (misfire).

[0056] The barrel exit sensors of the invention preferably use standardprinted circuit board (PCB) techniques utilizing SIOC packaged ICs, andchip capacitors and resistors.

[0057] The barrel exit sensors of the invention were evaluated usingboth a drop tower and a simulation station. The drop tower consists of ametal tube made of materials and dimensions similar to a 120 mm mortartube. Alternatively, a modified 120 mortar tube may be used. The testapparatus allowed for mechanical acceleration to achieve high velocitiesfor meaningful testing of the barrel exit sensor.

[0058] The simulation test station was based on using an arbitrarywaveform generator, coupled to a discharge-capacitor driven currentsource to simulate the transient of a much faster barrel exit than thatachievable using a drop tower configuration. In principle thissimulation station accurately reproduce the magnetic field perturbationof a gun barrel exit at speeds in excess of 5,000 m/s, a velocityactually achieved by some munitions such as the kinetic energy rod. Thisvelocity is well within the bandwidth limitations of the sensor of thepresent invention.

[0059] 60, 80, and 120 mm mortar tubes were tested. Barrel exitdetectability was enhanced for the larger mortar tubes by improving thesensor and circuitry specifically for the larger mortar by using fluxguides, optimized geometry and signal processing techniques. The sensorwas able to detect the edge of the larger mortar tubes during barrelexit under simulated conditions.

[0060] Programs were performed related to GMR sensors for applicationsin both safing and fuzing, and in the use of GMR sensors and sensorarrays for nondestructive evaluation. In the area of safing and fuzingit was shown that the sensor can be used to detect revolutions in a 40mm round during live fire testing. The sensor provided information thatenabled an on-munition system to determine barrel exit, munitionvelocity, and range.

[0061] Tests with mortars were conducted. A sensor was made that wasable to detect barrel exit in a 60 mm mortar. Live fire tests confirmedthe utility of the sensor. In addition to sensor and circuit design,mechanical shock testing, and environmental testing were performed withgood results.

[0062] Signal conditioning and readout electronics were also developed.This resulted in tunnel junction GMR sensor arrays for NDE. The sensorelements developed were only 10 microns on a side, yet delivered 7% (ARin a 2 Oe field with nominal resistance near 10 k). Signal conditioningand readout electronics for the sensors were also developed.

[0063] Sensors for Fuze Applications

[0064] As described previously, the present invention providestechnology to measure barrel exit, spin velocity, and range using GMRsensors detecting the earth's magnetic field. Sensor systems werefabricated for live-fire testing. Tests with the 40 mm spinning roundwere done. Three (3) data recorder/spin sensor assemblies werefabricated, tested and potted into 40 mm back shells. Each final pottedtest unit was numbered 1, 2 and 3. Once the operation of the datarecorder and spin sensor were individually functionally verified, thetwo PCBs were interconnected and tested (assembly shown in FIGS. 6 and7).

[0065] Prior to triggering and recording, the data recorder was poweredand armed. This was accomplished through a 7.5 v battery or power supplysource, laptop computer and an RS-232 interface. This setup is shown inFIG. 8. The computer communicates to the data recorder through theRS-232 interface and cable. The data recorder microprocessor firmwareprogram is a self-contained program that performs BIT functions, arming,data upload, sampling rate and record time selection. The computer usedthe Windows program “Hyperterminal” to communicate with the datarecorder. This program provides communication with the data recorder foroperator parameter entry as well as data upload “receive text file” modeto upload the data from the data recorder to a file on the hard disk.This text was then imported to “Excel” to plot the data to a graph (seeFIG. 9).

[0066] Flight Distance Calculations During Field Testing

Predicted Flight Distance==Muzzle Velocity*Flight Time=831*0.25=207.75ft

Turns Calculated Flight Distance=# of Turns*4 ft/Turn=51.5*4=206.0 ft%  Error = ((Predicted  Flight  Distance − Turns  Calculated  Flight  Distance)/Predicted  Flight  Distance) * 100 = ((207.75 − 206)/207.75) * 100% = 0.84%

[0067] Safing and Arming Sensor—Counter Munitions

[0068] The present invention also relates to advanced magnetic safingand arming (S&A) sensor technology based on giant magnetoresistive (GMR)sensors (see FIG. 10). The counter munition would initially be guided byradar which would also sense the munition. Once the counter munitionneared its target the GMR sensor(s) would pinpoint its location and setthe needed time delay on the fuze for maximum destructive power to thetarget. The present invention provides a sensor that can detect incomingmunitions such as the KE rod or TOW missile. The sensor providesproximity information that is used by ISP to destroy the incomingmunition before it reaches its target (e.g., a tank).

[0069] The sensor is mounted in the nose of the counter munition. Itsenses the local field strength. When nearing an incoming munition, itdetects a change in the magnetic field strength due to permanentmagnetic fields generated by ferromagnetic metal in the munition. Italso detects the change in the Earth's magnetic field due to thevariations in the field lines caused by metal in the munition. Changesin field strength detected by the sensor provides the proximityinformation needed to detonate the counter munition at the mostadvantageous time

[0070] One approach to increase sensitivity is to place a permanentmagnet near the sensor as a biasing magnet. As the sensor approaches themetallic munition, the bias point changes due to the ferromagnetic metalin the munition.

[0071] An active sensor with an oscillation frequency selected for thetype of munition can be used. The sensor is inductively programmed atthe time of counter munition launch for the type of incoming munition,based on radar information from the ISP system. A coil wrapped aroundthe nose or any surface of the counter munition emanates anelectromagnetic frequency selected for the type of incoming munition.The magnetic field properties generated by the coil change as thecounter munition nears its target, thus providing the information neededfor optimum detonation of the counter munition.

[0072] In all of these cases, multiple sensors can be used fortriangulation. This increases angular sensitivity, and provide moredetailed information about the incoming munition which can be used toenhance the performance of the counter munition.

[0073] The sensor preferably has the following properties:

[0074] Reponse time: 1 ns

[0075] Bandwidth: >1 GHz

[0076] Signal to noise ratio: depending on application CAN be >1000

[0077] Power consumption: ˜3V at 2 mA for passive sensor

[0078] Field of view: 3600

[0079] Environmental ruggedness: The sensor and circuit on a PCB havebeen tested to 100,000 g in live fire tests of rotating rounds;temperature tolerance of sensor has been demonstrated at −1800 C to+1500 C

[0080] Size and weight: Current fuze circuit and sensor fit on round PCB25 mm diameter that weighs 1.8 grams. Could be smaller as a hybridcircuit. Actual sensor is approximately 100×100 microns.

[0081] The sensor technology has a wide range of uses including barrelexit and velocity for mortars, and range for spinning rounds. It alsocan be used for trajectory measurements and proximity to metallictargets. The sensor system has highly desirable characteristicsincluding: extremely small size, low power operation, high shockresistance, wide temperature range, and extremely fast response time.Its operation is based on the local magnetic fields, making it highlyreliable and independent of other system such as GPS. The sensor systembenefits munitions programs by offering a high-performance, low-costalternative for arming and safing applications for both non-rotating androtating munitions.

[0082] Targeting Sensor

[0083] The present invention also provides a targeting sensor. It uses asingle sensor or an array of sensors (see FIG. 17). The sensors provideinformation regarding the location and/or proximity of the munition toits target. Relative signal strengths and frequency responses are usedto identify types of targets for positive identification or IFF(identification friend or foe).

[0084] Medical Imaging Sensor

[0085] This type of sensor or sensor array can also be used in themedical field. For example, it can be used to measure electromagneticactivity in the heart or brain. It can be used as a sensor in the fieldof biomagnetics. It can also be used in nuclear magnetic resonanceimaging. The ability of the sensor to detect magnetic fields in a singleplane or line makes it suitable for use in imaging skin defects ortissue anomalies. It can also be used for imaging low volume pointdefects. The small signals from small volume defects can be extremelydifficult to detect using standard NMR imaging because the signals fromthe small volume area are overshadowed by those from larger volume areaswhich contain more hydrogen, and therefore produce larger signals.

[0086] Target Identification

[0087] There are many different types of magnetic information producedby vehicles and like mechanical systems, all of which can be used toaccurately identify and characterize the source of the field. Amongthese sources are: perturbations of the earth's field by a movingmetallic object or vehicle; fields associated with electric motors;fields associated with generators and alternators; fields associatedwith spark plugs, wires and coils; fields related to rapidly movingmetallic parts such as cooling fans, gears and motor parts; fieldsassociated with large masses of metals such as boat hulls, mines,trucks, aircraft, and tanks. Each source will produce characteristicamplitudes, frequencies and periodicity related to the layout of-vehicleand its speed when passing the sensor. By using an integrated approachto the analysis of the all the different types of magnetic fieldsgenerated, there will be considerable information available for accuratedetermination of the type of source and level of threat.

[0088] Vehicle Analysis and Differentiation

[0089] In the case of passive detection of the perturbations in theearth's magnetic field caused by a moving metallic object (vehicle), theresulting magnetic signature is produced by the shape and metalliccomposition of the vehicle. For example, the x, y and z components ofthe magnetic signature of a moving object can be detected by sensorsburied underneath the surface of a road or beneath the surface of a bodyof water. In the case of a road, at the surface of the road, themagnitude of the magnetic field produced by a vehicle will beapproximately the same as the earth's magnetic field or ˜0.5 Oe. Thesensor must have sensitivity that is high enough to measure magneticfields that could be at or below the earth field. This calls for highsensitivity at low frequencies (slow moving vehicles will produce fieldinformation down to 1 Hz.). Sensors according to the present inventionoffer a signal to noise ratio of ˜20,000 at 0.5 Oe and 1 Hz. This typeof sensor has both the sensitivity and low noise characteristicsrequired for the measurement of the small magnetic fields that will beencountered by the buried sensors.

[0090] Using three sensors and vector analysis, it is possible to obtainthree-dimensional information concerning length, width and height of thevehicle. Wide vehicles such as tanks produce a much larger y componentresponse compared to a thinner automobile or bus. The amplitude of thesignal provides information concerning the metallic composition of thevehicle. For example a bulldozer, tank, or armored personnel carrierwould contain more steel than an auto or school bus. Another approach isto determine the distance between the front of the vehicle and the firstaxle, or simply counting axles.

[0091] Sensor arrays are preferred to enhance the ability of the systemto characterize the vehicle. For example, it is possible to analyzestrips of information. The additional sensors also improve the amount ofdata available so that statistical analysis can be used to effectivelyreduce noise and increase vehicle confirmation accuracy.

[0092] To supplement the information produced by the perturbation of theearth's field, several other magnetic field sources are preferablyexamined. In the case of magnetic fields emanating from generators,electric motors, and fast moving mechanical parts, the frequency, fieldamplitude and position of the source in the vehicle can be used toidentify the vehicle. These sources will generally have higherfrequencies than the perturbation of the magnetic fields. Thisdifference in frequency will allow the sources to be separated forindividual analysis. The field magnitude may also be much larger due tothe high currents and/or voltages produced. This type of analysis canprovide information such as the number of motors, how large they are,where they are located, and what their power output is. All of thisprovides valuable information for vehicle characterization.

[0093] Moving mechanical components such as fans, gears, and moors partswill also provide magnetic field information. Again, frequency andamplitude information are likely to be differentiated from othercomponents of the vehicle. In general, they will be higher frequency andlower noise than both the electrical components of the vehicle and thesignals generated by electrical components. One can determine thedistance of a cooling fan from the front of the vehicle or the number ofgears on a flywheel. This sort of information will help detail thecharacteristics of the vehicle.

[0094] Another potentially overlooked information source inherent tomany military and construction vehicles is its communication system.Devices such as radio and telephone produce significant amounts of highfrequency electromagnetic information. One can detect radio waves usinga sensor according to the present invention with high signal to noiseratio. One can both measure the frequency of the signal and possiblydemodulate the signal and determine the content of the communication.

[0095] Obtaining all of this information requires a fast and highlyefficient data collection scheme. Sensors according to the presentinvention used in conjunction with computerized data collection andanalysis circuitry can operate at low power levels (˜3 mw when active)yet can collect data at 20 mHz. Such circuitry can fit on a printedcircuit board about the size of a quarter dollar, and has been subjectedto 100,000 g by firing on board a 40 mm round. It is preferred toinclude a power management capability to reduce power consumption to 0.3microamps at 3 v by using one of the sensors, such as a seismic sensor,to activate the circuitry, permitting the magnetic field sensor systemto remain functional for over ten years using a single coin cellbattery.

[0096] Sensor integration will be an important aspect of a sensor systemaccording to the invention. The information generated by severalmagnetic field sensors can be analyzed using several differenttechniques. Each sensor will produce information concerning fieldamplitude, frequency and position of the source. This independentinformation will provide information to decide the type of vehicle beingscanned. It can also be used to compare to a magnetic field signaturefor known vehicles or types of vehicles. It can also be used as nodes ina neural network. In the case of biosensors, a neural network can beused to improve the selectivity of the array for molecular analysis. Formagnetoresistance sensors, such analysis can be used to correlatefrequency, amplitude and phase data to produce high spatial information,three-dimensional images of magnetic field sources.

[0097] A second aspect of sensor fusion is in improving power managementand the functional lifetime of the sensor. One approach is to use datafrom the seismic sensors to activate the magnetic sensors. Anotherapproach is activating the magnetic field sensors for a few microsecondseach second (the sensors and circuit activate in ˜1 ns) to determine thepresence of a threat, and the need to fully activate the entire system.The combination of the data output from the different types of sensorsin the system will also improve the characterization of the vehicle andincrease the probability of it being able to perform as desired.

[0098] Magnetoresistance Sensors and Sensor Arrays For NondestructiveEvaluation (NDE)

[0099] The magnetoresistance sensors and arrays of the present inventioncan also be employed for NDE of conductive components (see FIG. 19,sample results in FIG. 18). Sensors according to the present inventioncan be used to detect, scan, and image eddy currents in defectivemetallic components, such as sheet metal parts or pipe welds. This isparticularly valuable for evaluation of items with small feature sizesuch as printed circuit boards, flip chips, and printed circuit tapes.An array of sensors with dimensions on the order of 1 to 50 microns candetect defects that are micron-sized or smaller.

[0100] Because magnetic fields pass through materials it is possible toform three-dimensional images of materials. The depth of penetration ofan induced magnetic field is dependant on field frequency and theelectronic properties of the material. This phenomena will provide depthinformation at any given magnetic field induction frequency.

[0101] Using a variety of different frequencies enhances the ability toperform depth analysis. When evaluating objects such as printed circuitboards, images made at different frequencies will obtain data at variousdepths in the material. It is possible to use high frequencies toexamine only the top layer(s) of the printed circuit board because atsufficiently high frequencies the field will not penetrate beyond thefirst layer of the printed circuit board. Lower frequencies will allowanalysis deeper into the material. By collecting data at a variety offrequencies, it is possible to separate the upper layers of a material(or printed circuit board) from the lower layers. In this way depthanalysis can be performed. For example, it would allow non-destructiveevaluation of individual layers in a printed circuit board.

[0102] Tunnel junction GMR sensor arrays for NDE were developed. Thesensor elements developed were only 10 microns on a side, yet delivered7% (AR in a 2 Oe field with nominal resistance near 10 k). Signalconditioning and readout electronics for the sensors may also beemployed. Other types of GMR and CMR sensors can also be used ratherthan the preferred tunnel junction type of GMR device. The source of themagnetic field may be induced eddy currents, electrical current flowthrough a trace, wire, or component, or another source.

[0103] U.S. Pat. No. 6,150,809, entitled “Giant Magnetorestive Sensorsand Sensor Arrays for Detection and Imaging of Anomalies in ConductiveMaterials” relates to magnetic and electromagnetic nondestructiveevaluation. This technology is based on a synergistic combination of atraditional eddy-current coil or permanent magnet and a unique magneticsensor based on a class of materials known as giant magnetoresistors.The result is a sensor exhibiting substantially higher field sensitivityand spatial resolution when compared with traditional methods. Sincethese sensors directly sense the magnetic field, rather than changes inthe field as is the case for coils, they can be operated with highsensitivity at very low frequencies and even with DC generated fields.

[0104] A handheld NDE instrument was developed. This system was able todetect third layer (0.065″ 2024T3 per layer) cracks without the need forbench-top instrumentation. The present invention is a handheld NDE unitalong with a variety of sensors as shown in FIG. 11. This unit providesfour different graphical data display modes and is capable of resolvingdefects to a depth of approximately 0.2″ using the smaller diameterprobes and to a depth of approximately 0.4″ using the larger probe.

[0105] Current GMR detectors include several configurations. Most arepackaged using molded urethane. The process begins with a sensor, coiland flux focusing (if applicable) alignment on a metrology station. Thealigned assembly, along with the electronics subsystem, sapphire wearsurface and electrical connector, is then encased in color-codedurethane. This process provides a rugged and compact package for thesensor and eliminates costly machining.

[0106] The sensors are typically driven with a constant-current AC drivebetween 50 Hz and 25 kHz. At 1 kHz the ⅜″ diameter sensors can easilyresolve EDM cuts less than 0.25″ in length through 0.195″ of 2024T3. Alarger, ¾″version of this sensor has be used to image anomalies to over0.4″ in 6061T6.

[0107] Two-dimensional imaging arrays of GMR elements have been designedand units have been fabricated. Functional arrays consisting of 196tunnel-junction sensors (14×14). The individual sensors are only a fewsquare microns in area and are positioned on a grid with asensor-to-sensor spacing of approximately 210 microns. The active areaof the entire 14×14 element array is less than 3 mm on a side (9 mm2).FIG. 12 shows a photo of one of the imaging array prototypes. In thisphoto the magnetic field generation has been removed. Large (4″×4″)arrays provide for real-time imaging of deeply imbedded defects andcorrosion.

[0108] High resolution images of magnetic fields were obtained byperforming raster scans of various test samples. FIG. 13 shows an 11 kHzscan of first and second layer rivet heads in an aluminum sheet metalsection simulating an aircraft wing. FIG. 14 shows 100 micron wide cutsin an aluminum sheet metal sample. This data demonstrates the extremelyhigh signal-to noise ratio obtainable with the GMR sensor technology ofthe present invention.

[0109]FIG. 15 shows an image of a corrosion test sample provided by theFederal Aviation Administration, Nondestructive Inspection ValidationCenter (FAA/AANC). The sample is a 0.06″ thick, 2024T3 plate with anominal 10% uniform mass loss corrosion region on one side. The imagecorresponds to a scan performed on the side opposite the corrodedregion. The boundary of the corroded region, as well as the pittingwithin the corroded region is sharply defined in the image and thesignal-to-noise ratio in excess of 100 for these features.

[0110] A fusion of magnetic vision (MV) and other types of machinevision is useful for applications such as sorting metals or locatingdefects. Information from both types of images, taken together, can bethe only effective way to provide the total amount of information neededof complete analysis. The images from a MV system and an optical system(for example) can be put together (fused) in software. The optical imagemight, for example, detect the full shape or color or differentiateplastic from metal. The MV system might, for example, provide detailedinformation about the metal parts, not possible with the optical visionsystem by itself. The optical system would identify materials such asplastic that the MV system would not be able to detect at all. Thefusion of the two data sets would provide more information than eitheralone, and would be necessary for some applications.

[0111] Detection of Conductive Materials

[0112] The present invention also provides a magnetometer (see FIG. 16)for detecting conductive materials either on the surface or underneathother materials such as earth or water (e.g., mines). This sensor ishandheld or operated from a vehicle or aircraft. It operates in a DCdetection mode or with oscillating magnetic fields. Permanent magnets orflux concentrators are used to enhance the signal detected by thesensor.

[0113] This type of sensor may be used to locate ships, submarines, andother vessels. It can also be used to detect electrical currents flowingthrough PCB traces or IC components. It can be used to measure theamplitude of electrical currents. It can also be used to detect breaksin electrical conductors which would result in low or non-existentcurrent flow. As such, it can be used for inspection of many types ofcircuitry and wiring.

[0114] Impact Sensing

[0115] GMR sensors are magnetorestrictive. During impact such sensorsare compressed and will output a signal characteristic of impact.

[0116] Magnetic Field Tracking for Guidance

[0117] GMR sensors according to the invention may also be used for moresophisticated means of guidance of ordnance. A sensor can use a map oflocal magnetic fields to determine position and direction of a munitionor any moving object such as an aircraft or truck. Flying objects may bedetected by looking for response to an emitted electromagnetic field(active sensing) or looking for eddy currents output by aircraft as theytraverse the earth's magnetic field (passive sensing).

[0118] Although the invention has been described in detail withparticular reference to these preferred embodiments, other embodimentscan achieve the same results. Variations and modifications of thepresent invention will be obvious to those skilled in the art and it isintended to cover in the appended claims all such modifications andequivalents. The entire disclosures of all references, applications,patents, and publications cited above are hereby incorporated byreference.

What is claimed is:
 1. A magnetic field sensing system for locatingdefects in objects in two or three dimensions, said system comprising asensor comprising a magnetoresistance detector and means for sensing ata plurality of frequencies.
 2. The system of claim 1 wherein said meansfor sensing provides for sensing defects at a plurality of depths in theobjects.
 3. The system of claim 2 wherein the objects are printedcircuit boards.
 4. A magnetic field sensing system for imaging objectscomprising a magnetoresistance detector, means for non-magnetic imaging,and means for analyzing images produced by both said magnetoresistancedetector and said means for non-magnetic imaging.
 5. The system of claim4 wherein said means for non-magnetic imaging comprises optical imagingmeans.
 6. A system for mechanical system identification comprising amagnetoresistance detector.
 7. The system of claim 6 wherein said systemcomprises a system for vehicle identification.
 8. The system of claim 6additionally comprising means for analyzing output of saidmagnetoresistance detector and comparing results to knowncharacteristics of items selected from the group consisting of:perturbations of the earth's field by a moving metallic object orvehicle; fields associated with electric motors; fields associated withgenerators and alternators; fields associated with spark plugs, wiresand coils; fields related to rapidly moving metallic parts; and fieldsassociated with large masses of metals.
 9. The system of claim 6 whereinsaid system comprises at least three magnetoresistance detectors. 10.The system of claim 6 wherein said magnetoresistance detector detectsperturbations of the earth's magnetic field by the mechanical system.11. The system of claim 6 wherein said magnetoresistance detectordetects magnetic fields generated by electromagnetic components of themechanical system.
 12. The system of claim 6 wherein saidmagnetoresistance detector detects radio waves generated by themechanical system.
 13. A magnetic field sensing method for locatingdefects in objects in two or three dimensions, the method comprising thesteps of providing a sensor comprising a magnetoresistance detector andsensing at a plurality of frequencies.
 14. The method of claim 13wherein the sensing step senses defects at a plurality of depths in theobjects.
 15. The method of claim 14 wherein the objects are printedcircuit boards.
 16. A magnetic field sensing method for imaging objects,the method comprising the steps of providing a magnetoresistancedetector, employing means for non-magnetic imaging, and analyzing imagesproduced by both the magnetoresistance detector and the means fornon-magnetic imaging.
 17. The method of claim 16 wherein the means fornon-magnetic imaging comprises optical imaging means.
 18. A method formechanical system identification, the method comprising the steps ofproviding a magnetoresistance detector and using the detector to sensecharacteristics of a passing mechanical system.
 19. The method of claim18 wherein the passing mechanical system is a vehicle.
 20. The method ofclaim 18 additionally comprising the step of analyzing output of themagnetoresistance detector and comparing results to knowncharacteristics of items selected from the group consisting of:perturbations of the earth's field by a moving metallic object orvehicle; fields associated with electric motors; fields associated withgenerators and alternators; fields associated with spark plugs, wiresand coils; fields related to rapidly moving metallic parts; and fieldsassociated with large masses of metals.
 21. The method of claim 18wherein the providing step comprises providing at least threemagnetoresistance detectors.
 22. The method of claim 18 wherein in theusing step the magnetoresistance detector detects perturbations of theearth's magnetic field by the mechanical system.
 23. The method of claim18 wherein in the using step the magnetoresistance detector detectsmagnetic fields generated by electromagnetic components of themechanical system.
 24. The method of claim 18 wherein in the using stepthe magnetoresistance detector detects radio waves generated by themechanical system.